Re: [PATCH] Btrfs: only exclude supers in the range of our block group V2

[Josef Bacik <jbacik@fusionio.com>]

On Wed, Apr 24, 2013 at 09:48:27PM -0600, Liu Bo wrote:
> On Wed, Apr 24, 2013 at 10:48:09AM -0400, Josef Bacik wrote:
> > On Wed, Apr 24, 2013 at 08:43:21AM -0600, Liu Bo wrote:
> > > On Wed, Apr 24, 2013 at 09:00:16AM -0400, Josef Bacik wrote:
> > > > On Wed, Apr 24, 2013 at 02:57:40AM -0600, Liu Bo wrote:
> > > > > On Tue, Apr 23, 2013 at 02:48:54PM -0400, Josef Bacik wrote:
> > > > > > If we fail to load block groups halfway through we can leave extent_state's on
> > > > > > the excluded tree.  This is because we just lookup the supers and add them to
> > > > > > the excluded tree regardless of which block group we are looking at currently.
> > > > > > This is a problem because we remove the excluded extents for the range of the
> > > > > > block group only, so if we don't ever load a block group for one of the excluded
> > > > > > extents we won't ever free it.  This fixes the problem by only adding excluded
> > > > > > extents if it falls in the block group range we care about.  With this patch
> > > > > > we're no longer leaking space when we fail to read all of the block groups.
> > > > > > Thanks,
> > > > > > 
> > > > > > Signed-off-by: Josef Bacik <jbacik@fusionio.com>
> > > > > > ---
> > > > > > V1->V2: fixed a slight problem where i should have been comparing to the end of
> > > > > > hte block group not the begining.
> > > > > > 
> > > > > >  fs/btrfs/extent-tree.c |   24 +++++++++++++++++++++---
> > > > > >  1 files changed, 21 insertions(+), 3 deletions(-)
> > > > > > 
> > > > > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> > > > > > index b441be3..a81f689 100644
> > > > > > --- a/fs/btrfs/extent-tree.c
> > > > > > +++ b/fs/btrfs/extent-tree.c
> > > > > > @@ -270,9 +270,27 @@ static int exclude_super_stripes(struct btrfs_root *root,
> > > > > >  			return ret;
> > > > > >  
> > > > > >  		while (nr--) {
> > > > > > -			cache->bytes_super += stripe_len;
> > > > > > -			ret = add_excluded_extent(root, logical[nr],
> > > > > > -						  stripe_len);
> > > > > > +			u64 start, len;
> > > > > > +
> > > > > > +			if (logical[nr] > cache->key.objectid +
> > > > > > +			    cache->key.offset)
> > > > > > +				continue;
> > > > > > +
> > > > > > +			if (logical[nr] + stripe_len <= cache->key.objectid)
> > > > > > +				continue;
> > > > > 
> > > > > hmm...I just doubt that these two cases can happen.
> > > > > 
> > > > > btrfs_rmap_block() ensures that logical[nr] will be larger than
> > > > > cache->key.objectid.
> > > > > 
> > > > > Am I missing something?
> > > > 
> > > > Yeah, we can still get ranges that are past the end of the cache, just put a
> > > > printk in there and you'll see it happen.  Now it's not likely that a logical
> > > > will be less than the start but better safe than sorry.  Thanks,
> > > > 
> > > 
> > > But if it's really past the end of the cache, there might be something wrong in
> > > btrfs_rmap_block() IMO.
> > > 
> > > Ok, I'll dig it somehow.
> > > 
> > 
> > It's doing it right, we just loop through all of the supers, which we have no
> > idea where they show up logically.  It's not a problem with rmap, it's doing the
> > right thing, we just need to add this extra check because rmap is not bounded in
> > its logical search.  Thanks,
> 
> Sorry, I still didn't get how this happens...
> 
> I'll try to create new btrfs with raid0, raid1, raid10, raid5, raid6...
> 
> Could you please show me the testcase or something so that I can persuade
> myself?
> 

Ok I see what happened, I was using an old btrfs-image which makes one big chunk
to cover the entire file system, so that is how I was getting logical values
higher than the cache.  So not a normal case for sure, but since it is possible
for it to happen in a bad file system situation we should still leave it.
Thanks,

Josef